Method for making a high current low profile inductor

ABSTRACT

A high current, low profile inductor includes a conductor coil surrounded by magnetic material to form an inductor body. The inductor coil is formed from a flat plate which is cut into a sine-shaped configuration and then is folded in accordion fashion to create a helical coil.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No. 11/409,651 filed Apr. 24, 2006; which is a divisional application of application Ser. No. 10/244,777, filed Sep. 16, 2002, now U.S. Pat. No. 6,946,944; which is a continuation of Ser. No. 09/546,859 filed Apr. 10, 2000, now U.S. Pat. No. 6,449,829; which is a divisional of application Ser. No. 09/271,748, filed on Mar. 18, 1999, now U.S. Pat. No. 6,135,375

This application is also a divisional application of application Ser. No. 11/409,651 filed Apr. 24, 2006; which is a divisional of application Ser. No. 10/244,777 filed Sep. 16, 2002, now U.S. Pat. No. 6,946,944; which is a continuation of application Ser. No. 09/547,155, filed Apr. 11, 2000, now U.S. Pat. No. 6,460,244; which is a divisional of application Ser. No. 08/963,224 filed Nov. 3, 1997, now U.S. Pat. No. 6,204,744; which is a continuation of application Ser. No. 08/503,655 filed Jul. 18, 1995, now abandoned.

The Specification and Drawings of application Ser. No. 09/547,155, now U.S. Pat. No. 6,460,244, are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an inductor coil structure and method for making same. The coil structure of the present invention is preferably for use in a high current low profile inductor commonly referred to by the designation IHLP. However, the particular coil structure may be used in other types of inductors.

Inductor coils have in the prior art been constructed from various shapes of materials formed into various helical shapes. However, there is a need for an improved inductor coil structure which is simple to manufacture and which provides an efficient and reliable inductance coil.

Therefore, a primary object of the present invention is the provision of an improved inductor coil structure and method for making same.

A further object of the present invention is the provision of an inductor coil structure which can be used in a high current low profile inductor having no air spaces in the inductor, and which includes a magnetic material completely surrounding the coil.

A further object of the present invention is the provision of an inductor coil structure which includes a closed magnetic system which has self-shielding capability.

A further object of the present invention is the provision of an inductor coil structure which maximizes the utilization of space needed for a given inductance performance so that the inductor can be of a minimum size.

A further object of the present invention is the provision of an improved inductor coil structure which is smaller, less expensive to manufacture, and is capable of accepting more current without saturation than previous inductor coil structures.

A further object of the present invention is the provision of an inductor coil structure which lowers the series resistance of the inductor.

SUMMARY OF THE INVENTION

The foregoing objects may be achieved by a high current low profile inductor comprising a conductor coil having first and second coil ends. A magnetic material surrounds the conductor coil to form an inductor body. The inductor coil comprises a plurality of coil turns extending around a longitudinal coil axis in an approximately helical path which progresses axially along the coil axis. The coil turns are formed from a flat plate having first and second opposite flat surfaces, at least a portion of each of the flat surfaces of the coil turns facing in a axial direction with respect to the coil axis.

The method for making the inductor includes taking an elongated plate conductor having a first end, a second end, opposite side edges, opposite flat surfaces, and a longitudinal plate axis. A plurality of slots are cut in each of the opposite side edges of the plate conductor so as to form the plate conductor into a plurality of cross segments extending transversely with respect to the plate axis and a plurality of connecting segments extending approximately axially with respect to the plate axis. The connecting segments connect the cross segments together into a continuous conductor which extends in a sine shaped path. As used herein the term “sine shaped” refers to any shape which generally conforms to a sine curve, but which is not limited to a continuous curve and may include apexes, squared off corners or other various shapes.

After cutting the slots in the opposite side edges of the plate conductor the connecting segments are bent along one or more bend axes extending transversely with respect to the plate axis so as to form the plate conductor into a plurality of accordion folds, each of which comprise one of the cross segments and a portion of one of the connecting segments. In the resulting structure, the cross segments and the connecting segments form a continuous conductor coil of approximate helical shape having first and second opposite ends.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is a perspective view of the inductor constructed in accordance with the present invention and mounted upon a circuit board.

FIG. 2 is a pictorial view of the coil of the inductor before the molding process.

FIG. 3 is a pictorial view of the inductor of the present invention after the molding process is complete, but before the leads have been formed.

FIG. 4 is an end elevational view taken along line 4-4 of FIG. 2.

FIG. 5 is an elevational view taken along lines 5-5 of FIG. 4.

FIG. 6 is a perspective view of an elongated conductor blank from which the inductor coil is formed.

FIG. 7 shows the blank of FIG. 6 after the formation of slots extending inwardly from the opposite edges thereof.

FIG. 8 is a view similar to FIG. 7, showing the first folding step in the formation of the inductor coil of the present invention.

FIG. 9 is a side elevational view showing the same folding step shown in FIG. 8.

FIG. 10 is a view similar to 8 and showing a second folding step in the process for making the inductor coil of the present invention.

FIG. 11 is an inverted pictorial view of the inductor after it has been pressed, but before the leads have been formed.

FIG. 12 is a view similar to FIG. 11 showing the inductor after partial forming of the leads.

FIG. 13 is a view similar to FIGS. 11 and 12 showing the final forming of the leads.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings the numeral 10 generally designates an inductor of the present invention mounted upon a circuit board 12. Inductor 10 includes an inductor body 14 having a first lead 16 and a second lead 18 extending therefrom and being folded over the opposite ends of body 14. Leads 16, 18 are soldered or otherwise electrically connected on the circuit board 12.

Referring to FIG. 2, the inductor coil of the present invention is generally designated by the numeral 20. Leads 16, 18 form the ends of coil 22. Between leads 16, 18 are a plurality of L-shaped coil segments 26 each comprising a horizontal leg 28 and a vertical leg 30. Vertical leg 30 terminates at a connecting segment 32 which is folded over at approximately 180° so as to create an accordion like configuration for inductor coil 20. The L-shaped coil segments are connected together to form a helical coil having an open coil center 34 extending along a longitudinal coil axis 36.

FIGS. 6-10 show the process for making the coil 20. Initially as shown in FIG. 6 a blank flat conductor plate 50 formed of copper or other electrically conductive material includes: first and second ends 52, 54; a pair of opposite flat surfaces 56; and a pair of opposite side edges 58, 60.

FIG. 7 shows the first step in forming the coil 20. In this step a plurality of slots 62, 64 are cut in the opposite edges 58, 60 respectively of the blank flat plate 50. Various cutting methods may be used such as stamping or actual cutting by laser or other cutting tools known in the art.

Upon completion of the cutting operation, the blank 50 is transformed into an elongated sine shaped body formed from a plurality of cross segments 66 extending transversely to the longitudinal axis of plate 50 and a plurality of connecting segments 67 extending axially with respect to the longitudinal axis of plate 50. The segments 66, 67 form a continuous sine shaped configuration as shown in FIG. 7.

FIG. 8 shows the next step in forming the coil 20. The end 52 is folded over at an angle of 180° to form the 180° angle bend 63 in the first connecting segment 67. FIG. 10 shows a second bend 65 which is in the next connecting segment 67. Bends 63, 65 are in opposite directions, and are repeated until an accordion like structure is provided similar to that shown in FIG. 5.

In FIG. 5 the coil 20 includes opposite ends 16, 18 which are formed from the opposite ends 52, 54 of blank 50. The cross segments 66 of blank 50 form the first horizontal legs 28 of coil 20, and the connecting segments 67 of blank 50 form the second vertical legs 30 and the connecting segments 32 of coil 20.

An example of a preferred material for coil 20 is a copper flat plate made from OFHC copper 102, 99.95% pure.

The magnetic molding material of body 14 is comprised of a powdered iron, a filler, a resin, and a lubricant. The preferred powdered material is manufactured by BASF Corporation, 100 Cherryhill Road, Parsippany, N.J. under the trade designation Carbonyl Iron, Grade SQ. This SQ material is insulated with 0.875% mass fraction with 75% H₃P04.

An epoxy resin is also added to the mixture, and the preferred resin for this purpose is manufactured by Morton International, Post Office Box 15240, Reading, Pa. under the trade designation Corvel Black, Number 10-7086.

In addition a lubricant is added to the mixture. The lubricant is a zinc stearate manufactured by Witco Corporation, Box 45296, Huston Tex. under the product designation Lubrazinc W.

Various combinations of the above ingredients may be mixed together, but the preferred mixture is as follows:

-   -   1,000 grams of the powdered iron.     -   3.3% by weight of the resin.     -   0.3% by weight of the lubricant.         The above materials (other than the lubricant) are mixed         together and then acetone is added to wet the material to a         mud-like consistency. The material is then permitted to dry and         is screened to a particle size of −50 mesh. The lubricant is         then added to complete the material 82. The material 82 is then         ready for pressure molding.

The next step in the process involves compressing the material completely around the coil 20 so that it has a density produced by exposure to pressure of from 15 to 25 tons per square inch. This causes the powdered material 82 to be compressed and molded tightly completely around the coil so as to form the inductor body 14 shown in FIG. 1 and in FIGS. 11-13.

At this stage of the production the molded assembly is in the form which is shown in FIG. 11. After baking, the leads 16, 18 are formed or bent as shown in FIGS. 12 and 13. The molded assemblies are then baked at 325° F. for one hour and forty-five minutes to set the resin.

When compared to other inductive components the IHLP inductor of the present invention has several unique attributes. The conductive coil, lead frame, magnetic core material, and protective enclosure are molded as a single integral low profile unitized body that has termination leads suitable for surface mounting. The construction allows for maximum utilization of available space for magnetic performance and is magnetically self-shielding.

The unitary construction eliminates the need for two core halves as was the case with prior art E cores or other core shapes, and also eliminates the associated assembly labor.

The unique conductor winding of the present invention allows for high current operation and also optimizes magnetic parameters within the inductor's footprint.

The manufacturing process of the present invention provides a low cost, high performance package without the dependence on expensive, tight tolerance core materials and special winding techniques.

The magnetic core material has high resistivity (exceeding 3 mega ohms) that enables the inductor as it is manufactured to perform without a conductive path between the surface mount leads. The magnetic material also allows efficient operation up to 1 MHz. The inductor package performance yields a low DC resistance to inductance ratio of two milliohms per microHenry. A ratio of 5 or below is considered very good.

The unique configuration of the coil 20 reduces its cost of manufacture. Coil 20 may be used in various inductor configurations other than IHLP inductors.

In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms are employed these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in the form and the proportion of parts as well as in the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims. 

1. A method for making a high current low profile inductor comprising: forming an inductor element comprising a coil having and open center and an outside surface, the coil also having first and second coil ends; making a dry mixture comprising a dry resin and an insulated dry powdered magnetic powder; compressing the dry mixture around the outside surface of the coil and within the open center of the coil to create an inductor body without liquefying the dry mixture, whereby the inductor body engages the coil both within the coil open center and also the coil outside surface; the compressing step being done at least at a pressure of 15 tons per square inch.
 2. The method according to claim 1 wherein the compressing step is done at from 15 tons per square inch to 25 tons per square inch.
 3. The method according to claim 1 wherein a filler and a lubricant are added to the mixture before the compressing step is started.
 4. A method for making a high current low profile inductor comprising: forming an inductor element comprising a coil having and open center and an outside surface, the coil also having first and second coil ends; insulating a dry magnetic iron powder; making a dry mixture comprising a dry resin and a dry insulated magnetic iron powder; compressing the mixture in a single step while the mixture is dry around the outside surface of the coil and within the open center of the coil to create an inductor body, whereby the inductor body engages the coil both within the coil open center and also the coil outside surface.
 5. The method of claim 4 wherein the insulating step comprises using phosphoric acid.
 6. The method of claim 4 and further comprising wetting the mixture of resin and iron powder and then drying the wetted mixture before the compressing step; and screening the mixture to a predetermined particle size after the drying step and before the compressing step.
 7. The method of claim 6 and further comprising screening the mixture to a particle size of −50 mesh.
 8. A method for making a high current low profile inductor comprising: forming an inductor element comprising a coil having and open center and an outside surface, the coil also having first and second coil ends; making a dry mixture comprising a dry resin and an insulated dry powdered magnetic powder; compressing the dry mixture around the outside surface of the coil and within the open center of the coil to create an inductor body without liquefying the dry mixture, whereby the inductor body engages the coil both within the coil open center and also the coil outside surface; baking the compressed inductor body, whereby the baked inductor body is self shielding, has a high resistivity exceeding 3 mega ohms, operates up to 1 MHz, and yields a low DC resistance to inductance ratio of two milliohms per micro Henry. 